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The pressure effect on the Curie temperature and exchange striction of Cr2S3 and Cr2Te3
Journal of Magnetism and Magnetic Materials 70 (1987) 223-224 North-Holland, Amsterdam
223
T H E P R E S S U R E E F F E C T O N T H E CURIE T E M P E R A T U R E AND E X C H A N G E S T R I C T I O N OF Cr2S 3 AND Cr2Te 3 M. Y U Z U R I *, T. K A N O M A T A * * and T. K A N E K O * ** • Yokohama National University, Yokohama, Japan • * Tohoku Gakuin University, Miyagi, Japan • * * Tohoku Unit, ersity, Sendai, Japan
The pressure derivative of T~ was found to be 1.0 d e g / k b a r for Cr2S 3 and - 1 . 7 8 d e g / k b a r for Cr2Te 3. The volume exchange striction was found to be negative for Cr2S 3 and positive for Cr,Te 3. From these results, it was found that the exchange striction was dominant in the a-axis direction.
1. Introduction The intermetallic compounds Cr2S 3 and CrzTe 3 are known to be ferrimagnetic with a N6el temperature (T N) of about 130 K and ferromagnetic with a Curie temperature (T~) of about 180 K. Both compounds have a NiAs structure with ordered arrangement of vacant chromium site. The magnetic moment of the chromium atom is 3~B, which corresponds to Cr 3+ ionic state. One of the present authors has investigated the concentration dependence of the Curie temperature and the lattice parameters a and c for pseudobinary compounds Cr2S 3 ~Te~ [1]. As seen in fig. 1, the results showed (1) OTN/Ox < O, Oa/Ox > O, ~c/Ox > 0 and OV/Ox > 0 on the Cr2S 3 side and OTJOx > O, Oa/Ox > 00c/Ox > 0 and OV/ax > 0 on the Cr2Te 3 side. From the above results, we can expect that aTN/OV (or OTN/Op) is negative (or
Cr=S~_, Te x Q
d~ /dV
d~ /dV>O
( dTt, / d P > O )
(dTc / d P < O )
/
CO
Cr2Sa
-'-) X
---.fl--
~
Cr2Tea
Fig. 1. Magnetic and lattice parameters versus concentration x in Cr2S 3 ,Te,.
positive) for C r 2 S 3 and aT~/OV (or OTc/ap) is positive (or negative) for Cr2Te 3. Furthermore, we can also expect negative volume exchange striction for C r 2 S 3 and positive one for Cr2Te 3 from the standpoint that the strength of exchange interaction depends on the interatomic distance. In this study, the pressure effect on the Curie temperature and the exchange striction for Cr2S 3 and Cr2Te 3 are investigated.
2. Experimental results and discussion The pressure change of the Curie temperature was measured at pressures up to 6 kbar. The determination of the Curie temperature was made by measuring the temperature dependence of magnetic permeability. The results are shown in fig. 2. The Curie temperature increases linearly for C r 2 S 3 and decreases linearly for Cr2T % with applied pressure. The pressure derivative of the Curie temperature was obtained to be 1.0 d e g / k b a r for C r 2 S 3 and - 1 . 7 8 d e g / k b a r for Cr2Te 3 and their sign is consistent with that expected from the concentration dependence of the Curie temperature and the lattice parameters mentioned above. The exchange striction for both compounds were measured in the temperature range from 77 to 320 K by X-ray diffraction technique. As shown in figs. 3 and 4, the volume exchange striction was found to be negative for Cr2S 3 and positive for CrzTe 3. These results are also consistent with those expected from the results described above. As seen from figs. 3 and 4, the dominant part of the volume exchange striction, V(T), is one a(T),
0304-8853/87/$03.50 ~ Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
224
M. Yuzuri et al. / T and exchange striction of ('rzS s and ('r2Te ~
120
80.0
g 17o g
Cr2Te3
~ 79.5
Cr2Te~ &o
V
s > 79.C 165
E 3.92
6.05
o
v
o
;
2
;
4
6.00 ~ ×
.-
160
110
x
;
eU
5.95
3.91
Pressure(k bar)
Fig. 2. Pressure dependences of the Curie temperature of Cr2S 3 and Cr2Te 3.
along the a-axis. So, we can conclude from all the data mentioned above that the dependency of atomic distance of exchange interaction, J , in a-axis direction is dominant in the pressure effect of T~ for Cr2S 3 and for Cr2Te 3.
v ~
Cr2S~ o<
"d 56.0 E _= 0
> 55.7
v(T f ~
c ×
5.54 ca
Ac(T)
× i
111
3.41
200
300 T(K)
Fig. 4. Lattice p a r a m e t e r s versus temperatute of Cr2Te ~.
From the magnetic structure of both compounds [2,3], J is considered to be negative for Cr2S 3 and positive for Cr2Te 3. Therefore, the sign of the exchange striction in the a-axis direction is negative for Cr2S 3 and positive for Cr2Te3, but the distance dependence of Z,, dJ,,/da is positive for both compounds. In the compound CrSb with the NiAs structure, the chromium atom is also in the Cr 3+ ionic state and d J , / d a is positive [4]. It is considered interesting to examine systematically the atomic dependence of Ja between Cr 3' ion in the compounds with a NiAs type structure.
?
3.42
.2
100
o
-AafT)I~ I
References
o o
|
10 0
I
5.53
I
l
200
I
300 T(K)
Fig. 3. Lattice parameters versus temperature of Cr2S ~.
[1] M. Yuzuri and T. Yusuki, J. Magn. Magn. Mat. 54 (1986) 923. [2] E.F. Bertaut, J. Cohen, M.B. L a m b e r t - A n d r o n and P. Mollard, J. Phys. 29 (1968) 813. [3] T J . A . Popma, C. Haas and Van Laar, J. Phys. Chem. Solids, 32 (1971) 581. [4] S. Abe. T. Kaneko, M. Ohashi, H. Yoshida and K. Kamigaki, J. Phys. Soc. J a p a n 53 (1984) 27(/3.
223
T H E P R E S S U R E E F F E C T O N T H E CURIE T E M P E R A T U R E AND E X C H A N G E S T R I C T I O N OF Cr2S 3 AND Cr2Te 3 M. Y U Z U R I *, T. K A N O M A T A * * and T. K A N E K O * ** • Yokohama National University, Yokohama, Japan • * Tohoku Gakuin University, Miyagi, Japan • * * Tohoku Unit, ersity, Sendai, Japan
The pressure derivative of T~ was found to be 1.0 d e g / k b a r for Cr2S 3 and - 1 . 7 8 d e g / k b a r for Cr2Te 3. The volume exchange striction was found to be negative for Cr2S 3 and positive for Cr,Te 3. From these results, it was found that the exchange striction was dominant in the a-axis direction.
1. Introduction The intermetallic compounds Cr2S 3 and CrzTe 3 are known to be ferrimagnetic with a N6el temperature (T N) of about 130 K and ferromagnetic with a Curie temperature (T~) of about 180 K. Both compounds have a NiAs structure with ordered arrangement of vacant chromium site. The magnetic moment of the chromium atom is 3~B, which corresponds to Cr 3+ ionic state. One of the present authors has investigated the concentration dependence of the Curie temperature and the lattice parameters a and c for pseudobinary compounds Cr2S 3 ~Te~ [1]. As seen in fig. 1, the results showed (1) OTN/Ox < O, Oa/Ox > O, ~c/Ox > 0 and OV/Ox > 0 on the Cr2S 3 side and OTJOx > O, Oa/Ox > 00c/Ox > 0 and OV/ax > 0 on the Cr2Te 3 side. From the above results, we can expect that aTN/OV (or OTN/Op) is negative (or
Cr=S~_, Te x Q
d~ /dV
d~ /dV>O
( dTt, / d P > O )
(dTc / d P < O )
/
CO
Cr2Sa
-'-) X
---.fl--
~
Cr2Tea
Fig. 1. Magnetic and lattice parameters versus concentration x in Cr2S 3 ,Te,.
positive) for C r 2 S 3 and aT~/OV (or OTc/ap) is positive (or negative) for Cr2Te 3. Furthermore, we can also expect negative volume exchange striction for C r 2 S 3 and positive one for Cr2Te 3 from the standpoint that the strength of exchange interaction depends on the interatomic distance. In this study, the pressure effect on the Curie temperature and the exchange striction for Cr2S 3 and Cr2Te 3 are investigated.
2. Experimental results and discussion The pressure change of the Curie temperature was measured at pressures up to 6 kbar. The determination of the Curie temperature was made by measuring the temperature dependence of magnetic permeability. The results are shown in fig. 2. The Curie temperature increases linearly for C r 2 S 3 and decreases linearly for Cr2T % with applied pressure. The pressure derivative of the Curie temperature was obtained to be 1.0 d e g / k b a r for C r 2 S 3 and - 1 . 7 8 d e g / k b a r for Cr2Te 3 and their sign is consistent with that expected from the concentration dependence of the Curie temperature and the lattice parameters mentioned above. The exchange striction for both compounds were measured in the temperature range from 77 to 320 K by X-ray diffraction technique. As shown in figs. 3 and 4, the volume exchange striction was found to be negative for Cr2S 3 and positive for CrzTe 3. These results are also consistent with those expected from the results described above. As seen from figs. 3 and 4, the dominant part of the volume exchange striction, V(T), is one a(T),
0304-8853/87/$03.50 ~ Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
224
M. Yuzuri et al. / T and exchange striction of ('rzS s and ('r2Te ~
120
80.0
g 17o g
Cr2Te3
~ 79.5
Cr2Te~ &o
V
s > 79.C 165
E 3.92
6.05
o
v
o
;
2
;
4
6.00 ~ ×
.-
160
110
x
;
eU
5.95
3.91
Pressure(k bar)
Fig. 2. Pressure dependences of the Curie temperature of Cr2S 3 and Cr2Te 3.
along the a-axis. So, we can conclude from all the data mentioned above that the dependency of atomic distance of exchange interaction, J , in a-axis direction is dominant in the pressure effect of T~ for Cr2S 3 and for Cr2Te 3.
v ~
Cr2S~ o<
"d 56.0 E _= 0
> 55.7
v(T f ~
c ×
5.54 ca
Ac(T)
× i
111
3.41
200
300 T(K)
Fig. 4. Lattice p a r a m e t e r s versus temperatute of Cr2Te ~.
From the magnetic structure of both compounds [2,3], J is considered to be negative for Cr2S 3 and positive for Cr2Te 3. Therefore, the sign of the exchange striction in the a-axis direction is negative for Cr2S 3 and positive for Cr2Te3, but the distance dependence of Z,, dJ,,/da is positive for both compounds. In the compound CrSb with the NiAs structure, the chromium atom is also in the Cr 3+ ionic state and d J , / d a is positive [4]. It is considered interesting to examine systematically the atomic dependence of Ja between Cr 3' ion in the compounds with a NiAs type structure.
?
3.42
.2
100
o
-AafT)I~ I
References
o o
|
10 0
I
5.53
I
l
200
I
300 T(K)
Fig. 3. Lattice parameters versus temperature of Cr2S ~.
[1] M. Yuzuri and T. Yusuki, J. Magn. Magn. Mat. 54 (1986) 923. [2] E.F. Bertaut, J. Cohen, M.B. L a m b e r t - A n d r o n and P. Mollard, J. Phys. 29 (1968) 813. [3] T J . A . Popma, C. Haas and Van Laar, J. Phys. Chem. Solids, 32 (1971) 581. [4] S. Abe. T. Kaneko, M. Ohashi, H. Yoshida and K. Kamigaki, J. Phys. Soc. J a p a n 53 (1984) 27(/3.